Searching for GEMS: Discovery and Characterization of Two Brown Dwarfs Around M Dwarfs*
Abstract Brown dwarfs bridge the gap between stars and planets, providing valuable insight into both planetary and stellar-formation mechanisms. Yet the census of transiting brown-dwarf companions, in particular around M-dwarf stars, remains incomplete. We report the discovery of two transiting brown dwarfs around low-mass hosts using a combination of space- and ground-based photometry along with near-infrared radial velocities. We characterize TOI-5389Ab ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>68</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mi mathvariant="normal">J</mml:mi> </mml:msub> </mml:math> ) and TOI-5610b ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>40</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>4</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mi mathvariant="normal">J</mml:mi> </mml:msub> </mml:math> ), two moderately massive brown dwarfs orbiting early M-dwarf hosts ( T eff = 3569 ± 59 K and 3618 ± 59 K, respectively). For TOI-5389Ab, the best fitting parameters are period P = 10.40046 ± 0.00002 days, radius <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">BD</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.82</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.031</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.033</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> R J , and low eccentricity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>e</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.096</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.0046</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0027</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . In particular, this constitutes one of the most extreme substellar-stellar companion-to-host mass ratios of q = 0.150. For TOI-5610b, the best-fitting parameters are period P = 7.95346 ± 0.00002 days, radius <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">BD</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.88</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.031</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.031</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> R J , and moderate eccentricity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>e</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.35</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.012</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.011</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . Both targets are expected to have shallow, but potentially observable, occultations: ≲500 ppm in the Johnson K band. A statistical analysis of M-dwarf/BD systems reveals for the first time that those at short orbital periods ( P < 13 days) exhibit a dearth of 13 M J < M BD < 40 M J companions ( q < 0.1) compared to those at slightly wider separations.
Authors
- Samuel Halverson (ORCID: https://orcid.org/0000-0003-1312-9391)
- Joe Philip Ninan (ORCID: https://orcid.org/0000-0001-8720-5612)
- Henry A. Kobulnicky (ORCID: https://orcid.org/0000-0002-4475-4176)
- Scott A. Diddams (ORCID: https://orcid.org/0000-0002-2144-0764)
- Caleb I. Cañas (ORCID: https://orcid.org/0000-0003-4835-0619)
- Chad F. Bender (ORCID: https://orcid.org/0000-0003-4384-7220)
- Jessica E. Libby-Roberts (ORCID: https://orcid.org/0000-0002-2990-7613)
- Tera N. Swaby (ORCID: https://orcid.org/0000-0002-5817-202X)
- Arvind F. Gupta (ORCID: https://orcid.org/0000-0002-5463-9980)
- Shubham Kanodia (ORCID: https://orcid.org/0000-0001-8401-4300)
- Arpita Roy (ORCID: https://orcid.org/0000-0001-8127-5775)
- Maxwell Moe (ORCID: https://orcid.org/0000-0002-0870-6388)
- Christian Schwab (ORCID: https://orcid.org/0000-0002-4046-987X)
- Paul M. Robertson (ORCID: https://orcid.org/0000-0003-0149-9678)
- Andrea S. J. Lin (ORCID: https://orcid.org/0000-0002-9082-6337)
- Guđmundur Stefánsson (ORCID: https://orcid.org/0000-0001-7409-5688)
- Suvrath Mahadevan (ORCID: https://orcid.org/0000-0001-9596-7983)
- William D. Cochran (ORCID: https://orcid.org/0000-0001-9662-3496)
- Andrew Monson (ORCID: https://orcid.org/0000-0002-0048-2586)
- Alexander Larsen (ORCID: https://orcid.org/0000-0002-2401-8411)
Institutions
- Tata Institute of Fundamental Research (IN)
- California Institute of Technology (US)
- University of Wyoming (US)
- Goddard Space Flight Center (US)
- Pennsylvania State University (US)
- U.S. National Science Foundation (US)
- Jet Propulsion Laboratory (US)
- University of Arizona (US)
- University of Colorado Boulder (US)
- Carnegie Institution for Science (US)
- University of California, Irvine (US)
- Planetary Systems (United States) (US)
- NSF NOIRLab (US)
- The University of Texas at Austin (US)
- University of Amsterdam (NL)
- Macquarie University (AU)
Publication Details
- Journal
- The Astronomical Journal
- Published
- 2025-04-03
- DOI
- https://doi.org/10.3847/1538-3881/adbb54
- Citations
- 2
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 2.31
Funders
- Wyoming Space Grant Consortium